Export add-on error: rna_uiItemO: operator missing srna 'x.y'
The registration of the operator was broken. The bpy.utils.register_classes_factory() generates a register() and unregister() function for all supplied classes, but doesn't call them. There was also a , missing in the class tuple.

classes = (
    ExportUrchin,
)


def register():
    for cls in classes:
        bpy.utils.register_class(cls)
    bpy.types.TOPBAR_MT_file_export.append(menuFunc)


def unregister():
    for cls in classes:
        bpy.utils.unregister_class(cls)
    bpy.types.TOPBAR_MT_file_export.remove(menuFunc)